Slide-fastener stringers have been made heretofore with a pair of woven support tapes along juxtaposed edges of which are provided respective rows of spaced apart discrete or individual coupling elements of thermoplastic synthetic-resin material. The coupling elements can have arms which are clamped over the edge of the support tape and are joined together in a weld zone, a continuous support member, or plurality of such support members, extending along the row of coupling elements and, generally, forming part of the support tape. Weft yarns of the tape may pass over this continuous support member between adjacent fastener elements.
The fastener elements may also have coupling heads which interdigitate with the coupling heads of the other row upon movement of a slider along the stringer, the slider also serving to disengage the rows of coupling heads from one another.
The coupling elements of slide fasteners of this type generally are symmetrical with respect to the plane of the fastener. They can be shaped by bending initially substantially flat members into a U-shape so that the bight of the U forms the coupling head and the shanks of the U form the aforementioned arms.
The tapes may be composed of weft and warp yarns in a conventional manner and all of the weft yarns or only some of them can reach over the support member, which can also be a warp yarn, a cord or the like, to serve as attachment weft yarns. The support member can, as just noted, be a single-strand core engaged between the arms of the coupling element or disposed in a loop between the bight and the fusion point or zone. The support member can also consist of two or four or more so-called rope-ladder yarns which are embedded in the shanks of the fastener elements so as to be considered a multistrand support.
In all of the cases stated, the term "support" is intended to refer to single strand and multistrand, monofilament or multifilament, braided or other composite member which is disposed in the plane of symmetry of the coupling members or elements.
In general, however, the support will be a textile member which can be dimensioned and designed to withstand the transverse pull experienced by the finished fastener.
With slide fasteners of the type with which the present invention is concerned, several stress directions may be considered. The transverse direction mentioned previously is, of course, a direction transverse to the slide-fastener axis, i.e. perpendicular to the rows, usually in the slide-fastener plane. It is also important to consider the torsional stresses which act upon the discrete slide-fastener elements and tend to pivot them around the support, i.e. around the axis of the slide-fastener row, relative to the plane of the fastener. Torsional stress of this type can be considered to result from a force applied perpendicular to the plane of the slide fastener at the head of each coupling element and in a direction tending to twist the latter about the support.
The slide fastener is also exposed to various bending stresses, i.e. stresses applied transversely to the plane of the slide fastener in mounting the latter upon a garment, for example, or in use, a longitudinal stress during use of the slide fastener also being experienced.
In discrete-element slide fasteners (see German patent document No. 2,722,054) it is difficult to ensure torsional stability of the discrete fastener elements about the support and therefore relative to the plane of the fastener. To achieve this torsional stability it is known to form on the individual coupling elements thermoplastic members which extend longitudinally of the fastener or which may even be continuous to connect the coupling elements together. These thermoplastic members provide torsional stability either alone or in combination with the associated support member (see German patent document No. 2,741,780).
Unfortunately, with the latter technique for avoiding torsional distortion and increasing torsional stability, the fastener as a whole has an increased rigidity in that it cannot be as readily bent in or out of the fastener plane. The increased rigidity considerably reduces the break open strength of the closed slide fastener. This is because the stiffening elements produce stress and opening forces.